This invention relates to a fire-screening glazing panel comprising spaced layers of intumescent material sandwiched between sheets of vitreous material. The invention also relates to methods of manufacturing such panels.
Such panels can be used in the construction of exterior and interior building walls or partitions. They include transparent panels, useful for example as windows, and also transluscent and opaque panels which can be used in other parts of exterior or interior walls or partitions.
Fire-screening panels can be classified according to their effectiveness assessed in terms of the period of time for which one face of the panel can be exposed to a specified heating schedule, simulating fire, before the opposite face of the panel reaches a specified mean temperature or before any part of that opposite face reaches a certain temperature. One standard test is laid down in International Standard ISO 834 (Fire Resistance Tests--Elements of Building Construction) and a corresponding Belgian Standard NBN 713-020. This test is conducted by mounting the panel in a wall of a furnace in which the temperature is raised according to a specified formula and by measuring the period of time which elapses before any of three conditions occurs, namely (a) the panel ceases to provide a flame-proof and fume-proof barrier, (b) the mean temperature of the face of the panel directed to the exterior of the furnace rises above its initial (ambient) temperature by more than 140.degree. C. and (c) the temperature of any zone on that exterior face increases by more than 180.degree. C.
Various commercially available fire-screening panels comprising an intumescent layer sandwiched between two sheets of glass are able to survive that test for about 20 minutes. If glass fibre and wire mesh is added to the intumescent layer, the panels will survive the test for longer times.
In British patent specification No. 1 290 699 (BASF) it is proposed to provide a fire-screening panel comprising three sheets of glass secured to intervening intumescent layers. Those intumescent layers are able to form primary and secondary heat barriers in the event of the outbreak of fire on one side of the panel. It was found that the effectiveness of such a panel as a fire screen tends to increase with the thickness of the central glass sheet. This is in part because a thicker sheet is better able to prevent non-uniform heating of the secondary barrier-forming intumescent layer which is located behind that sheet. In our U.S. patent application Ser. No. 06/368,623 filed Apr. 15, 1982, such fire-screening panels are described wherein the central vitreous sheet is thicker than the outer sheets and has a thickness of at least 6 mm. Such a panel can have, for a given panel weight, a very high performance assessed by a fire-screening test such as that above referred to. If the outer sheets are identical, and the different intumescent layers are likewise identical, the panel is equally effective whichever of its faces is directed towards the fire.